--- /dev/null
+'use strict';
+
+var log = Math.log, LOG2E = Math.LOG2E;
+
+module.exports = function (x) {
+ if (isNaN(x)) return NaN;
+ x = Number(x);
+ if (x < 0) return NaN;
+ if (x === 0) return -Infinity;
+ if (x === 1) return 0;
+ if (x === Infinity) return Infinity;
+
+ return log(x) * LOG2E;
+};